The present invention concerns a converter for converting an a.c. voltage into a direct current, of the type comprising supply terminals, an input terminal and an output terminal.
The invention also concerns an oscillator circuit using said converter and comprising:
a sustain circuit including an input terminal, an output terminal, supply terminals, terminals for connecting a resonator, at least one active amplifier element, and polarization means for said active element, said means comprising a controllable current source connected in series with the controlled current path of the active element, said current source having a control terminal, and PA1 a regulator circuit acting on the control terminal of the current source in response to one of the following oscillation signals: input signal and output signal of the oscillator, so that the current source produces a current, the value of which falls in dependence on the amplitude of the pilot signal. PA1 the second elementary converter is so arranged as to provide a current i.sub.3 such that i.sub.3 =i.sub.30 -C.sub.1 1n(i.sub.1 /i.sub.10) in which i.sub.30 is a constant.
More particularly, the invention concerns oscillators having a very low level of current consumption, which are used in watches.
In oscillators of this kind, the regulator circuit maintains the amplitude of the oscillation signal at a low value in order to minimize the current consumption of the oscillator. However, the amplitude of the oscillation signal must be sufficient to permit that signal to be used in subsequent circuits such as: amplifiers, frequency divider, etc.
The article by E. A. VITTOZ "Quartz Oscillators For Watches," published in the proceedings of dixieme Congress International de Chronometrie (Tenth International Congress of Chronometry), Geneva, September 1979, volume 3, pages 131-140, describes an oscillator circuit of the above-indicated type. That known circuit, which is shown in FIG. 1, comprises a circuit 1 for sustaining the vibrations of a quartz resonator 2, and an amplitude regulator 3. The sustain circuit 1 comprises a MOS amplifier transistor 4 which is polarized by a resistor 5; the drain-source path of the transistor 4 is connected in series with that of another MOS transistor 6, between the terminals +V and -V of a supply voltage source. The transistor 6 acts as a controllable current source supplying power to the amplifier transistor 4 of the sustain circuit 1. The control terminal of the current source 6, which is the gate 6a of the transistor 6, receives a control signal which is provided by the regulator circuit 3 which itself receives, at its input 3a, by way of a decoupling capacitor 7, a signal which is referred to as a pilot signal for the oscillator and which appears at an input terminal 8 of the oscillator circuit. The regulator circuit 3 comprises four MOS transistors 9 to 12 which are connected in pairs in mirror image arrangement and which form a closed loop, the gain of which is limited by a resistance means formed by a fifth transistor 13. The regulator circuit 3 and the transistor 6 together form a converter for converting an a.c. input voltage into a direct current. By virtue of its very design, this converter requires a system for polarization of the transistors, comprising resistors 14 and 15 of very high value, which are formed by diodes produced in polycrystalline silicon. The result of this is that the known circuit can be produced only in a special form of circuit technology.
It is for this reason that an object of the present invention is in particular to propose a converter of that type, which can be produced by any form of circuit technology.